[libc-commits] [PATCH] D78612: [libc] Add sanitizer instrumentation to the SIMD strlen implementation.

[Evgenii Stepanov via Phabricator via libc-commits]

eugenis added a comment.

Calling __asan_region_is_poisoned on every word will have very poor performance under ASan. Not sanitizing that entire function would allow strlen to "hop over" inaccessible regions as long as the (alleged) end of the string is inside a valid allocation.

IMHO, running slow path under asan is not that bad, on the balance. The fast path is simple enough to verify by code inspection. Of course, we should only do this for truly simple and performance-critical functions.

Another option is to run the fast path unsanitized, and then check that the reported string bytes are actually accessible according to ASan. That's what the interceptors do. It is possible that the fast path escapes, hits an unmapped page and dies, but we have not seen in practice at all.


Repository:
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https://reviews.llvm.org/D78612